Method for fabricating a semiconductor device

ABSTRACT

A semiconductor device that improves the heat cycle resistance and power cycle resistance of a power module. An electrode member in which copper posts are formed in a plurality of perforations cut in a support made of a ceramic material is soldered onto a side of an IGBT where an emitter electrode is formed. By soldering the copper posts onto the electrode, heat generated in the IGBT is transferred to the electrode member and is radiated. In addition, even if a material of which the IGBT is made and copper differ in thermal expansivity, stress on a soldered interface is reduced and distortion is reduced. This suppresses the appearance of a crack. As a result, the heat cycle resistance and power cycle resistance of a power module can be improved.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims priority benefit toU.S. patent application Ser. No. 11/351,338, filed Feb. 10, 2006,pending, which application in turn is based upon and claims the benefitsof priority from the prior Japanese Patent Application No. 2005-052389,filed on Feb. 28, 2005, the entire contents of which are incorporatedherein by reference.

BACKGROUND

1. Field

This invention relates to a semiconductor device, an electrode member,and an electrode member fabrication method and, more particularly, to asemiconductor device used in a high-current high-voltage operatingenvironment, an electrode member used in such a semiconductor device,and a method for fabricating such an electrode member.

2. Description of the Related Art

In recent years power modules which can withstand high-currenthigh-voltage operating environments have been utilized in powerconverters, such as inverters/converters, for driving motors included inrobots, machine tools, electric vehicles, and the like. At present, suchpower modules are made up mainly of power semiconductor elements, suchas insulated gate bipolar transistors (IGBTs) and free wheeling diodes(FWDs) (see, for example, Japanese Unexamined Patent Publication No.2004-6603).

FIG. 17 is a schematic sectional view of an important part of aconventional power module.

FIG. 17 shows how an IGBT 100 is mounted in a power module. Usually anemitter electrode and a gate electrode (hereinafter referred to as the“emitter electrode etc.”) are formed on one side of the IGBT 100 and acollector electrode is formed on the other side of the IGBT 100. In FIG.17, it is assumed that the IGBT 100 is mounted with the emitterelectrode etc. upward and the collector electrode downward. As shown inFIG. 17, for example, the emitter electrode etc. formed on the upperside of the IGBT 100 are connected to corresponding external connectionterminals (not shown) by aluminum wires 101.

On the other hand, the collector electrode formed on the under side ofthe IGBT 100 is located on an insulating board 102 on a copper (Cu) heatradiation base (not shown and hereinafter referred to as the “copperbase”). The insulating board 102 is a ceramic plate made of, forexample, alumina which transmits heat well. Copper leaves 102 a and 102b are attached to both sides of the insulating board 102. The copperleaf 102 a attached to the upper side of the insulating board 102 issoldered onto the collector electrode and the copper leaf 102 b attachedto the under side of the insulating board 102 is soldered onto thecopper base. By adopting such a structure, electrical connection betweenthe IGBT 100 and the outside can be secured, insulation between the IGBT100 and a heat radiation system can be secured, and heat generated atoperating time can be transmitted to the copper base via the insulatingboard 102.

With the above conventional mounting method, heat can be radiated fromthe under side of the IGBT 100 via the insulating board 102 and thecopper base. However, only the thin aluminum wires 101 with a diameterof, for example, about 300 to 400 μm are connected to the upper side ofthe IGBT 100. In addition, the aluminum wires 101 generate heat as aresult of sending an electric current. Accordingly, it can hardly behoped that heat will be radiated from the upper side of the IGBT 100.Moreover, heat generated by the aluminum wires 101 may degrade thecharacteristics of the element. It is possible to use copper wireshaving high thermal conductivity in place of the aluminum wires 101.However, usually a certain number of wires corresponding to currentcapacity are ultrasonic-bonded onto the surface of the IGBT 100.Therefore, it is desirable that copper wires the hardness of which ishigher than that of the aluminum wires 101 should not be used so as notto damage the surface of the element.

FIG. 18 is a schematic sectional view of an important part of anotherconventional power module. Components in FIG. 18 that are the same asthose shown in FIG. 17 are marked with the same reference numerals anddetailed descriptions of them will be omitted.

To avoid the problems which arise by the use of an aluminum wire, anattempt shown in FIG. 18 has conventionally been made. In FIG. 18, acopper electrode 103 is soldered onto the upper side of an IGBT 100where an emitter electrode etc. are formed. An external connectionterminal 104 drawn out of the power module is bonded to the copperelectrode 103. By doing so, electrical connection between the IGBT 100and the outside is secured and heat can also be radiated from the upperside of the IGBT 100 via the copper electrode 103.

The same applies to the case where an FWD is mounted in a power module.For example, an anode electrode is formed on the upper side of the FWDand a cathode electrode is formed on the under side of the FWD. Aluminumwires are ultrasonic-bonded onto or a copper electrode is soldered ontothe upper side of the FWD. The under side of the FWD is soldered onto acopper leaf attached to an insulating board on a copper base.

However, the thermal expansivity of silicon (Si) which is the maincomponent of the IGBT or the FWD is about 2.6 ppm/° C. On the otherhand, the thermal expansivity of copper is about 17 ppm/° C. and ishigher than that of silicon. Therefore, if a copper electrode issoldered onto the upper side of the IGBT or the FWD in the above way inplace of aluminum wires with heat radiation taken into consideration, asoldered interface is subject to thermal stress at the time of heatcycling or power cycling because of the difference in thermalexpansivity between them. Distortion is caused by this thermal stress.As a result, a crack may appear and the target life of the power modulemay not be realized.

A crack may also appear under the IGBT or the FWD. That is to say, thethermal expansivity of the insulating board which is made of alumina andto the surface of which the copper leaf is attached is about 7 ppm/° C.This insulating board is soldered onto the copper base the thermalexpansivity of which is high. Accordingly, a soldered interface issubject to thermal stress because of the difference in thermalexpansivity between them. Distortion is caused by this thermal stressand a crack may appear. It is known that if heat cycling is performedbetween, for example, −40 and +125° C., a crack begins to appear due todistortion at the soldered interface between the insulating board andthe copper base after about 500 cycles.

The reason for using copper as a material for heat radiation bases inpower modules is that copper has good thermal conductivity (about 350W/(m·K)). However, to avoid the appearance of such a crack, a material,such as the one including copper molybdenum (CuMo) or aluminum siliconcarbide (AlSiC), the thermal expansivity of which is close to 7 ppm/° C.has been used in place of copper. The thermal expansivity of thesematerials is lower than that of copper, but their thermal conductivityis low (about 150 W/(m·K)). This characteristic is disadvantageous torecent small-loss IGBTs and FWDs. In addition, the costs ofmanufacturing heat radiation bases by using these materials are abouttwenty times higher than the manufacturing costs of copper bases.

SUMMARY

The present invention was made under the background circumstancesdescribed above. An object of the present invention is to provide asemiconductor device with great reliability in which heat internallygenerated is efficiently radiated and in which thermal stress on aninternal interface between members joined is reduced.

Another object of the present invention is to provide an electrodemember capable of efficiently radiating heat generated in asemiconductor device and reducing thermal stress on an internalinterface between members joined and a method for fabricating such anelectrode member.

In order to achieve the above first object, a semiconductor devicehaving a semiconductor element with an electrode on a surface isprovided. This semiconductor device comprises an electrode memberincluding an insulating support with a plurality of perforations whichpierce through principal planes and metal posts which are located in theplurality of perforations and which are joined to the electrode.

In order to achieve the above second object, an electrode member joinedto an electrode of a semiconductor device is provided. This electrodemember comprises an insulating support with a plurality of perforationswhich pierce through principal planes and metal posts located in theplurality of perforations.

In order to achieve the above second object, a method for fabricating anelectrode member joined to an electrode of a semiconductor device. Thiselectrode member fabrication method comprises the step of forming metalposts in a plurality of perforations which pierce through principalplanes of an insulating support by impregnating the insulating supportwith metal.

The above and other objects, features and advantages of the presentinvention will become apparent from the following description when takenin conjunction with the accompanying drawings which illustrate preferredembodiments of the present invention by way of example.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view of an important part of a powermodule according to a first embodiment of the present invention.

FIG. 2 is a schematic plan view of an important part of an example of anIGBT used in the power module according to the first embodiment of thepresent invention.

FIGS. 3A and 3B are schematic views of an electrode member according toa first embodiment of the present invention, FIG. 3A being a plan viewof the electrode member, FIG. 3B being a sectional view taken along theline a-a of FIG. 3A.

FIG. 4 is a schematic sectional view of an important part of anotherexample of the power module according to the first embodiment of thepresent invention.

FIG. 5 is a view for describing a heat radiation effect.

FIGS. 6A and 6B are schematic views of a power module using theelectrode member according to the first embodiment of the presentinvention, FIG. 6A being a plan view of the power module, FIG. 6B beinga sectional view taken along the line b-b of FIG. 6A.

FIGS. 7A and 7B are schematic views of an electrode member according toa second embodiment of the present invention, FIG. 7A being a plan viewof the electrode member, FIG. 7B being a sectional view taken along theline c-c of FIG. 7A.

FIGS. 8A and 8B are schematic views of an electrode member according toa third embodiment of the present invention, FIG. 8A being a plan viewof the electrode member, FIG. 8B being a sectional view taken along theline d-d of FIG. 8A.

FIGS. 9A and 9B are schematic views of an electrode member according toa fourth embodiment of the present invention, FIG. 9A being a plan viewof the electrode member, FIG. 9B being a sectional view taken along theline e-e of FIG. 9A.

FIGS. 10A and 10B are schematic views of an electrode member accordingto a fifth embodiment of the present invention, FIG. 10A being a planview of the electrode member, FIG. 10B being a sectional view takenalong the line f-f of FIG. 10A.

FIG. 11 shows an example of how an element is mounted on the electrodemember according to the fifth embodiment of the present invention.

FIGS. 12A and 12B are schematic views of an electrode member accordingto a sixth embodiment of the present invention, FIG. 12A being a planview of the electrode member, FIG. 12B being a sectional view takenalong the line g-g of FIG. 12A.

FIG. 13 shows an example of how an element is mounted on the electrodemember according to the sixth embodiment of the present invention.

FIGS. 14A and 14B are schematic views of an electrode member accordingto a seventh embodiment of the present invention, FIG. 14A being a planview of the electrode member, FIG. 14B being a sectional view takenalong the line h-h of FIG. 14A.

FIG. 15 shows an example of how an element is mounted on the electrodemember according to the seventh embodiment of the present invention.

FIGS. 16A and 16B are schematic views of an electrode member with acooling mechanism, FIG. 16A being a plan view of the electrode member,FIG. 16B being a sectional view taken along the line i-i of FIG. 16A.

FIG. 17 is a schematic sectional view of an important part of aconventional power module.

FIG. 18 is a schematic sectional view of an important part of anotherconventional power module.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention applied to, for example, a powermodule including an IGBT and an FWD will now be described in detail withreference to the drawings.

A first embodiment of the present invention will be described first.

FIG. 1 is a schematic sectional view of an important part of a powermodule according to a first embodiment of the present invention. FIG. 2is a schematic plan view of an important part of an example of an IGBTused in the power module according to the first embodiment of thepresent invention. FIGS. 3A and 3B are schematic views of an electrodemember according to a first embodiment of the present invention. FIG. 3Ais a plan view of the electrode member. FIG. 3B is a sectional viewtaken along the line a-a of FIG. 3A.

An emitter electrode 10 a and a gate electrode 10 b are formed on oneside of an IGBT 10 shown in FIG. 2. A collector electrode is formed onthe other side (not shown) of the IGBT 10. As shown in FIG. 1, with apower module including, for example, the IGBT 10, the collectorelectrode is soldered onto an insulating board 20 and the emitterelectrode 10 a is soldered onto an electrode member 30.

The insulating board 20 is made of a ceramic material, such as alumina,which conducts heat well. Copper leaves 21 and 22 which serve asconductor patterns and the like are attached to the surfaces of theinsulating board 20. The copper leaf 21 attached to the upper side ofthe insulating board 20 and the collector electrode formed on the IGBT10 are soldered together. The copper leaf 22 attached to the under sideof the insulating board 20 and a copper base (not shown) beneath thecopper leaf 22 used as a heat radiation base are soldered together. Whenthe power module is formed, the insulating board 20 is used forrealizing a dielectric strength of 5,000 volts or higher between theside where the IGBT 10 is mounted and the copper base side.

As shown in FIG. 3, the electrode member 30 comprises a support 31 whichis made of a ceramic material, such as alumina or cordierite, and inwhich a plurality of perforations 31 a which pierce through principalplanes are formed like an array and copper posts 32 formed by embeddingcopper in the plurality of perforations 31 a. As shown in FIG. 1, oneend of each copper post 32 included in the electrode member 30 issoldered onto the emitter electrode 10 a of the IGBT 10 and the otherend of each copper post 32 included in the electrode member 30 issoldered onto an external connection terminal and copper electrode(hereinafter simply referred to as the “copper electrode”) 40.

By joining the electrode member 30 to the emitter electrode 10 a, forexample, of the IGBT 10, heat generated in the IGBT 10 can be radiatedefficiently and distortion at an interface between the IGBT 10 and theelectrode member 30 caused by the difference in thermal expansionbetween the electrode member 30 and the IGBT 10 can be reduced. Thereason for this is as follows.

Copper (copper posts 32) which is included in the electrode member 30and which has high thermal conductivity is joined to the emitterelectrode 10 a of the IGBT 10, so heat radiation is promoted by thecopper posts 32. This is why heat generated in the IGBT 10 can beradiated efficiently. The thermal expansivity of alumina, being aceramic material, is about 7 to 8 ppm/° C. In particular, the thermalexpansivity of cordierite, being a ceramic material, is about 0.5 to 3ppm/° C. Accordingly, the thermal expansivity of the ceramic material ofwhich the support 31 is made is lower than that of copper (about 16.5 to18 ppm/° C.) of which the copper posts 32 are made. Therefore, when theelectrode member 30 thermally expands by heat generated in the IGBT 10,the support 31 restrains the thermal expansion of the copper posts 32and the thermal expansion of the electrode member 30 is suppressed. As aresult, the difference in thermal expansion between the IGBT 10 and theelectrode member 30 can be narrowed down at an interface where they arejoined. This is why distortion at the interface between the IGBT 10 andthe electrode member 30 can be reduced.

The electrode member 30 having the above structure is fabricated by, forexample, the following methods. A first method is as follows. First,ceramic powder is molded into a molding having a predetermined number ofperforations 31 a at predetermined positions by a press. The support 31is formed by burning the molding at a high temperature. The support 31is then impregnated with molten copper so that the molten copper willenter the perforations 31 a. Copper which has entered the perforations31 a is hardened. Copper which remains on the surface is removed by, forexample, polishing, if necessary. By doing so, the electrode member 30including the copper posts 32 is formed. A second method is as follows.The support 31 having the perforations 31 a is formed in the same way.Metal posts which are made of copper and which can be inserted into theperforations 31 a are prepared. The metal posts are inserted into theperforations 31 a of the support 31. The metal posts are integrated intothe support 31 by, for example, adhering the metal posts to the support31 or fitting the metal posts into the support 31. By doing so, theelectrode member 30 including the copper posts 32 is formed.

By locating the above electrode member 30 between the IGBT 10 and thecopper electrode 40, the IGBT 10 and the copper electrode 40 not onlyare thermally connected but also are electrically connected by a solderlayer (not shown) at the interface between the copper posts 32 and theemitter electrode 10 a and by a solder layer (not shown) at an interfacebetween the copper posts 32 and the copper electrode 40.

If comparison is made between the case where the electrode member 30 inwhich the copper posts 32 are formed in the above way and the IGBT 10are joined and the case where the copper electrode 40 on the entiresurface of which copper gets exposed and the IGBT 10 are joined, thejoin area of the two substances which differ in thermal expansivity inthe former case is smaller than in the latter case. In the former case,thermal stress on the solder layer at the interface which is created atthe time of heat being generated because of the difference between theirthermal expansivities is accordingly small. In addition, the solderlayer at the interface between the IGBT 10 and the electrode member 30not only connects them electrically and thermally but also lessens suchthermal stress. Moreover, the electrode member 30, together with thecopper electrode 40, functions as a heat sink, so heat can efficientlybe radiated from the upper side of the IGBT 10. As a result, distortionhardly occurs at the soldered interface and heat cycle resistance andpower cycle resistance can be improved.

As stated above, by soldering the electrode member 30 between the IGBT10 and the copper electrode 40, distortion at the soldered interfacebetween the IGBT 10 and the electrode member 30 can be reduced and heatgenerated in the IGBT 10 can be radiated efficiently. This significantlysuppresses the appearance of a crack at the soldered interface.

FIG. 4 is a schematic sectional view of an important part of anotherexample of the power module according to the first embodiment of thepresent invention.

In this first embodiment, a copper electrode 40 is joined onto anelectrode member 30. In this case, the copper electrode 40 is used as anexternal connection terminal as shown in FIG. 1. As shown in FIG. 4, thecopper electrode 40 may also be used as a conductor for connecting theelectrode member 30 to a second copper leaf 21 on an insulating board20.

A gate electrode 10 b (not shown) formed on an IGBT 10 is wired by, forexample, wire bonding. In the examples shown in FIGS. 1 through 4, theelectrode member 30 is almost equal in size to the emitter electrode 10a. However, the size of the electrode member 30 may be equal to that ofa chip of the IGBT 10 and the electrode member 30 may also be solderedonto the gate electrode 10 b. In this case, copper posts 32 connected tothe gate electrode 10 b are treated as a connection conductor for thegate electrode 10 b and the copper posts 32 should be wired by, forexample, wire boding or using the copper electrode 40.

FIG. 5 is a view for describing a heat radiation effect.

FIG. 5 shows temperature distribution obtained by passing a steady-statecurrent of 50 A_(dc) in the cases where the emitter electrode 10 a ofthe IGBT 10 is connected to the outside by wire bonding and whereexternal connection is made by using a lead frame structure includingthe electrode member 30 and the copper electrode 40. In FIG. 5, ahorizontal axis indicates distance (mm) in the direction of the depth ofthe power module (direction from the IGBT 10 to the insulating board 20)from a reference point for temperature measurement in each case. Avertical axis indicates temperature (° C.). T_(WB) indicates temperatureobtained in the case where wire bonding is used, T_(LF) indicatestemperature obtained in the case where a lead frame structure is used,and T_(j) indicates temperature at a position where a wire or theelectrode member 30 is joined to the IGBT 10.

As can be seen from FIG. 5, if wire bonding is used, T_(j) is 177.5° C.with the surface of the wire as a reference point for temperaturemeasurement (0 mm). On the other hand, the maximum value of T_(WB) is210.0° C. and is higher than T_(j). The temperature rises first from thereference point in the direction of the depth of the power module andthen goes down with an increase in the depth. This shows that heat isnot radiated properly from the inside, and suggests that heat issupplied from the wire itself.

If a lead frame structure is used, T_(j) is 155.0° C. with the surfaceof the copper electrode 40 pretty close to the electrode member 30 as areference point for temperature measurement (0 mm). On the other hand,the maximum value of T_(LF) is 152.4° C. and T_(LF) is lower than T_(j)at every depth including an area of the electrode member 30. Inaddition, compared with the case where wire bonding is used, thetemperature can significantly be lowered throughout. Therefore, it maysafely be said that the electrode member 30 and the copper electrode 40function as good conductors of heat internally generated.

The above descriptions have been given with the IGBT 10 as an example.If an FWD is included, a cathode electrode of the FWD is soldered onto,for example, the copper leaf 21 on the insulating board 20 and an anodeelectrode of the FWD is soldered onto the electrode member 30. By doingso, the same structure that was described above is obtained and the sameeffect that was described above can be achieved.

In the above examples, the electrode member 30 is located only on theemitter electrode 10 a or the anode electrode formed on the upper sideof the IGBT 10 or the FWD. However, the electrode member 30 may also belocated between the collector electrode or cathode electrode formed onthe under side of the IGBT 10 or the FWD and the copper leaf 21 attachedto the upper side of the insulating board 20 or between the copper leaf22 attached to the under side of the insulating board 20 and the copperbase.

FIGS. 6A and 6B are schematic views of a power module using theelectrode member according to the first embodiment of the presentinvention. FIG. 6A is a plan view of the power module. FIG. 6B is asectional view taken along the line b-b of FIG. 6A.

In a power module shown in FIG. 6, an IGBT 10 and a copper electrode 40are connected by an electrode member 30 and an FWD 50 and the copperelectrode 40 are connected by an electrode member 30. This is the samewith the above examples. In addition, the IGBT 10 and a copper leaf 21are connected by an electrode member 30, the FWD 50 and the copper leaf21 are connected by an electrode member 30, the copper electrode 40 andthe copper leaf 21 are connected by an electrode member 30, a copperelectrode 41 and the copper leaf 21 are connected by the electrodemember 30, and a copper electrode 42 and the copper leaf 21 areconnected by the electrode member 30. A copper leaf 22 and a copper base60 are also connected by an electrode member 30. By adopting such astructure, the same effect that was described above can be achieved.That is to say, heat generated in the IGBT 10 and the FWD 50 canefficiently be transmitted to the copper base 60. Furthermore, comparedwith the case where the electrode members 30 are not used, thermalstress on each soldered interface is relieved, distortion is reduced,and the appearance of a crack is suppressed.

A second embodiment of the present invention will now be described.

FIGS. 7A and 7B are schematic views of an electrode member according toa second embodiment of the present invention. FIG. 7A is a plan view ofthe electrode member. FIG. 7B is a sectional view taken along the linec-c of FIG. 7A. Components in FIGS. 7A and 7B that are the same as thoseshown in FIGS. 3A and 3B are marked with the same reference numerals anddetailed descriptions of them will be omitted.

As shown in FIG. 7B, an electrode member 30 a according to the secondembodiment of the present invention differs from the electrode member 30according to the first embodiment of the present invention in that acopper layer 33, being a conductor layer, is formed on one side of asupport 31.

For example, the electrode member 30 a having the above structure can befabricated by forming the copper layer 33 on one side of the support 31in which perforations 31 a are cut and by filling the perforations 31 awith copper by performing electroplating with the copper layer 33 as aseed. The copper layer 33 used as a seed can be formed by, for example,attaching a copper leaf to one side of the support 31 or performingelectroless plating. The electrode member 30 a may be fabricated byimpregnating the support 31 with molten copper and by removing copperonly on the other side (opposite to the side where the copper layer 33is to be left) of the support 31 by, for example, polishing until thesupport 31 gets exposed. This method is the same as that used forfabricating the electrode member 30 according to the first embodiment ofthe present invention.

By using the electrode members 30 a according to the second embodimentof the present invention in a power module, each element, such as anIGBT or an FWD, and a copper electrode can be connected electrically andthermally. Furthermore, each element and a copper leaf attached to theupper side of an insulating board can be connected electrically andthermally. In addition, a copper leaf attached to the under side of theinsulating board and a copper base can be connected electrically andthermally. Moreover, distortion at each soldered interface betweenmembers reduces and the appearance of a crack is suppressed. This is thesame with the electrode member 30 according to the first embodiment ofthe present invention. By locating the electrode member 30 a between anIGBT or an FWD and a copper electrode with the copper layer 33 opposedto the copper electrode or by locating the electrode member 30 a betweenan IGBT or an FWD and an insulating board with the copper layer 33opposed to the insulating board, for example, the same effect that isobtained by the electrode member 30 according to the first embodiment ofthe present invention can be achieved and electrical connection of theelectrode member 30 a can be secured two-dimensionally by the copperlayer 33. Accordingly, the electrode member 30 a according to the secondembodiment of the present invention is suitable for a place where notonly vertical continuity but also horizontal continuity is required.

A third embodiment of the present invention will now be described.

FIGS. 8A and 8B are schematic views of an electrode member according toa third embodiment of the present invention. FIG. 8A is a plan view ofthe electrode member. FIG. 8B is a sectional view taken along the lined-d of FIG. 8A. Components in FIGS. 8A and 8B that are the same as thoseshown in FIGS. 3A and 3B are marked with the same reference numerals anddetailed descriptions of them will be omitted.

As shown in FIG. 8B, an electrode member 30 b according to the thirdembodiment of the present invention differs from the electrode member 30according to the first embodiment of the present invention in that endportions of each copper post 32 protrude from both sides of a support31.

For example, the electrode member 30 b having the above structure can befabricated by forming the copper posts 32 in perforations 31 a cut inthe support 31 made of a ceramic material and by etching the support 31from the surface by chemical etching. For example, hydrofluoric acidwhich can selectively etch a ceramic in respect to metal may be used asetchant used for such chemical etching.

By using the electrode members 30 b according to the third embodiment ofthe present invention in a power module, members between which theelectrode member 30 b is located can be connected electrically andthermally. Moreover, distortion at each soldered interface betweenmembers reduces and the appearance of a crack is suppressed. This is thesame with the electrode member 30 according to the first embodiment ofthe present invention. In addition, the thickness of a solder layerwhich can relieve thermal stress created at the time of heat beinggenerated in an element can be increased by up to the length ofprotrusions of the copper posts 32 from the support 31, so theappearance of a crack at each soldered interface can be suppressedfurther.

In this example, end portions of each copper post 32 protrude from bothsides of the support 31. However, the electrode member 30 b may have astructure in which one end portion of each copper post 32 may protrudeonly from one side of the support 31.

A fourth embodiment of the present invention will now be described.

FIGS. 9A and 9B are schematic views of an electrode member according toa fourth embodiment of the present invention. FIG. 9A is a plan view ofthe electrode member. FIG. 9B is a sectional view taken along the linee-e of FIG. 9A. Components in FIGS. 9A and 9B that are the same as thoseshown in FIGS. 3A and 3B are marked with the same reference numerals anddetailed descriptions of them will be omitted.

As shown in FIG. 9B, an electrode member 30 c according to the fourthembodiment of the present invention differs from the electrode member 30according to the first embodiment of the present invention in that endportions of each copper post 32 protrude from both sides of a support 31and that the upper half and the lower half of each copper post 32 areinternally insulated from each other.

For example, the electrode member 30 c having the above structure isfabricated by one of the following two methods. A first method is asfollows. The copper posts 32 are formed first in perforations 31 a cutin the support 31. The support 31 is selectively etched from one side byusing, for example, hydrofluoric acid so that an end portion of eachcopper post 32 will protrude from this side of the support 31. A secondobject having the same structure as described above is fabricated in thesame way as described above. That is to say, with the second object,too, only one end portion of each copper post 32 protrudes from one sideof a support 31. These two objects are then, for example, adhered toeach other with an insulating plate 34 located between the other sidesof the supports 31 where the other end portion of each copper post 32does not protrude. By doing so, the electrode member 30 c shown in FIGS.9A and 9B can be fabricated.

A second method is as follows. Holes which do not pierce the support 31are made in both principal planes of the support 31. The copper posts 32are formed in the holes. By doing so, the electrode member 30 c in whichthe copper posts 32 formed in one side of the support 31 are internallyinsulated from the copper posts 32 formed in the other side of thesupport 31 by the one support 31 can integrally be fabricated. Thissaves the trouble of, for example, adhering the two objects to eachother with the insulating plate 34 between. To make end portions of eachcopper post 32 protrude from both sides of the support 31 as shown inFIG. 9B, the support 31 in which the copper posts 32 have been formedshould selectively be etched by using, for example, hydrofluoric acid.

With the electrode member 30 c according to the fourth embodiment of thepresent invention, the copper posts 32 formed in one side of the support31 are insulated from the copper posts 32 formed in the other side ofthe support 31 inside the electrode member 30 c. Therefore, by mountingan element, such as an IGBT or FWD, on one principal plane of theelectrode member 30 c and joining a copper base to the other principalplane of the electrode member 30 c as a heat radiation base, theelectrode member 30 c can be used as an insulating board for insulatingthe side on which the element is mounted from the side to which thecopper base is joined. Moreover, joining is performed with a pluralityof copper posts 32 and the thickness of a solder layer can be increasedby the length of an end portion of each copper post 32 which protrudesfrom a side of the support 31. As a result, distortion at each solderedinterface between members reduces and the appearance of a crack issuppressed.

In this example, end portions of each copper post 32 protrude from bothsides of the support 31. However, only one end portion of each copperpost 32 may protrude from one side of the support 31. In addition, endportions of each copper post 32 may not protrude from the support 31. Inthis case, however, a solder layer becomes thinner.

A fifth embodiment of the present invention will now be described.

FIGS. 10A and 10B are schematic views of an electrode member accordingto a fifth embodiment of the present invention. FIG. 10A is a plan viewof the electrode member. FIG. 10B is a sectional view taken along theline f-f of FIG. 10A. Components in FIGS. 10A and 10B that are the sameas those shown in FIGS. 3A and 3B are marked with the same referencenumerals and detailed descriptions of them will be omitted.

As shown in FIGS. 10A and 10B, an electrode member 30 d according to thefifth embodiment of the present invention differs from the electrodemember 30 according to the first embodiment of the present invention inthat end portions of each copper post 32 protrude from both sides of asupport 31, that the cross-sectional area (diameter) of a copper post 32at the center is the largest, that the cross-sectional area of a copperpost 32 gradually becomes smaller with an increase in the distance fromthe center, and that the density of copper posts 32 increases with anincrease in the distance from the center.

For example, the electrode member 30 d having the above structure isfabricated by the following method. Perforations 31 a are cut first inthe support 31. The diameter of a perforation 31 a at the center is thelargest and the diameter of a perforation 31 a becomes smaller with anincrease in the distance from the center. The density of theperforations 31 a increases with an increase in the distance from thecenter. The copper posts 32 is formed in the perforations 31 a. Thesupport 31 is selectively etched from the surface by chemical etching.As a result, the electrode member 30 d shown in FIGS. 10A and 10B can befabricated.

FIG. 11 shows an example of how an element is mounted on the electrodemember according to the fifth embodiment of the present invention.

Usually thermal stress on an edge portion of a soldered interfacebetween members is stronger than thermal stress on the center of thesoldered interface. Accordingly, as with the electrode member 30 daccording to the fifth embodiment of the present invention, copper posts32 each having a large cross-sectional area are formed in the centerwhere thermal stress is light and many copper posts 32 each having asmall cross-sectional area are formed in edge portions where thermalstress is strong. If a member 70 is soldered to the electrode member 30d, the formation of the above copper posts 32, combined with the effectof being able to increase the thickness of a solder layer (not shown) bythe length of an end portion of each copper post 32 which protrudes froma side of the support 31, suppresses the appearance of a crack at asoldered interface.

In this example, end portions of each copper post 32 protrude from bothsides of the support 31. However, only one end portion of each copperpost 32 may protrude from one side of the support 31. In addition, endportions of each copper post 32 may not protrude from the support 31.

A sixth embodiment of the present invention will now be described.

FIGS. 12A and 12B are schematic views of an electrode member accordingto a sixth embodiment of the present invention. FIG. 12A is a plan viewof the electrode member. FIG. 12B is a sectional view taken along theline g-g of FIG. 12A. Components in FIGS. 12A and 12B that are the sameas those shown in FIGS. 3A, 3B, 9A, and 9B are marked with the samereference numerals and detailed descriptions of them will be omitted.

As shown in FIG. 12B, an electrode member 30 e according to the sixthembodiment of the present invention differs from the electrode member 30c according to the fourth embodiment of the present invention in thatcopper posts 32 which protrude from both sides of a support 31 areconnected electrically and two-dimensionally to one another by copperlayers 35 a and 35 b, respectively, located on the insulating plate 34.

For example, the electrode member 30 e having the above structure isfabricated by the following method. Two objects which have the samestructure and in each of which only one end portion of each copper post32 protrudes from one side of a support 31 are fabricated. Theinsulating plate 34 on which the copper layers 35 a and 35 b are formedis then located between the other sides of the supports 31 where theother end portion of each copper post 32 does not protrude. This is thesame with the electrode member 30 c according to the fourth embodimentof the present invention.

FIG. 13 shows an example of how an element is mounted on the electrodemember according to the sixth embodiment of the present invention.Components in FIG. 13 that are the same as those shown in FIGS. 6A and6B are marked with the same reference numerals and detailed descriptionsof them will be omitted.

With the electrode member 30 e according to the sixth embodiment of thepresent invention, the copper posts 32 on one side and the copper posts32 on the other side are electrically connected to one another by thecopper layers 35 a and 35 b respectively. Accordingly, when an IGBT 10and an FWD 50 are soldered directly onto the electrode member 30 e,electrical connection can be secured on the side where the elements aremounted. Moreover, the electrode member 30 e itself can be used as aninsulating board for insulating the side where the elements are mountedfrom the side of a heat radiation base. As a result, it is possible tothermally connect members soldered with the electrode member 30 ebetween while securing two-dimensional electrical connection on eachside of the electrode member 30 e. In addition, distortion at eachsoldered interface between members can be reduced and the appearance ofa crack can be suppressed.

In this example, end portions of each copper post 32 protrude from bothsides of the support 31. However, only one end portion of each copperpost 32 may protrude from one side of the support 31. In addition, endportions of each copper post 32 may not protrude from the support 31. Inthis example, the copper layer 35 a is formed on one side of theinsulating plate 34 and the copper layer 35 b is formed on the otherside of the insulating plate 34. However, the copper layer 35 a or 35 bmay be formed only on one side of the insulating plate 34.

A seventh embodiment of the present invention will now be described.

FIGS. 14A and 14B are schematic views of an electrode member accordingto a seventh embodiment of the present invention. FIG. 14A is a planview of the electrode member. FIG. 14B is a sectional view taken alongthe line h-h of FIG. 14A. Components in FIGS. 14A and 14B that are thesame as those shown in FIGS. 3A, 3B, 9A, and 9B are marked with the samereference numerals and detailed descriptions of them will be omitted.

As shown in FIG. 14B, an electrode member 30 f according to the seventhembodiment of the present invention differs from the electrode member 30c according to the fourth embodiment of the present invention in thatone end portion of each copper post 32 protrudes from one side of asupport 31 and that the other end portion of each copper post 32 doesnot protrude from the other side of the support 31 and is connectedelectrically and two-dimensionally to the other end portions by a copperlayer 36.

For example, the electrode member 30 f having the above structure isfabricated by the following methods. A first method is as follows. Thecopper posts 32 are formed first in perforations 31 a cut in the support31. As described in the second embodiment, for example, the perforations31 a are cut and the copper layer 36 is formed by attaching a copperleaf to one side of the support 31 or performing electroless plating.The perforations 31 a are filled with copper by performingelectroplating with the copper layer 36 as a seed. By doing so, thecopper posts 32 are formed. Alternatively, the method of impregnatingthe support 31 with molten copper may be used. Two supports 31 arefabricated. With one support 31, the copper layer 36 is formed on oneside. With the other support 31, only one end portion of each copperpost 32 protrudes from one side. An insulating plate 34 is locatedbetween the sides of the two supports 31 where an end portion of eachcopper post 32 does not protrude. By doing so, the electrode member 30 fshown in FIGS. 14A and 14B can be fabricated.

FIG. 15 shows an example of how an element is mounted on the electrodemember according to the seventh embodiment of the present invention.Components in FIG. 15 that are the same as those shown in FIGS. 6A and6B are marked with the same reference numerals and detailed descriptionsof them will be omitted.

The electrode member 30 f according to the seventh embodiment of thepresent invention is located between elements, such as an IGBT 10 and anFWD 50, and a copper base 60. As a result, electrical connection can besecured on the side where the elements are mounted, and the electrodemember 30 f itself can be used as an insulating board for insulating theside where the elements are mounted from the side of the heat radiationbase. The copper layer 36 may be formed as a circuit pattern.

With the electrode member 30 f one end portion of each copper post 32protrudes from the support 31. If such structure is adopted, a coolingmechanism for passing a cooling medium between the electrode member 30 fand the copper base 60 can be used.

FIGS. 16A and 16B are schematic views of an electrode member with acooling mechanism. FIG. 16A is a plan view of the electrode member. FIG.16B is a sectional view taken along the line i-i of FIG. 16A. Componentsin FIGS. 16A and 16B that are the same as those shown in FIGS. 3A, 3B,6A, 6B, 9A, and 9B are marked with the same reference numerals anddetailed descriptions of them will be omitted.

If the electrode member 30 f according to the seventh embodiment of thepresent invention, for example, is used in a power module, a coolingmechanism for removing heat by passing a cooling medium 80 through aspace between the support 31 of the electrode member 30 f and a copperbase 60 is used as shown in FIGS. 16A and 16B. With this coolingmechanism, water, for example, is used as the cooling medium 80. Thecooling medium 80 is introduced from the outside of the power module,passes through the space between the support 31 of the electrode member30 f and the copper base 60, and is discharged again to the outside ofthe power module. As a result, heat in the power module can directly beremoved by using the cooling medium 80 and heat radiation is performedmore effectively. Therefore, distortion at each soldered interface canbe reduced and the appearance of a crack can be suppressed.

In FIGS. 16A and 16B, the description has been given with the case wherethe electrode member 30 f according to the seventh embodiment of thepresent invention is used in a power module as an example. However, theabove cooling mechanism is also applicable to the case where theelectrode member 30 b, 30 c, 30 d, or 30 e having structure in which anend portion of each copper post 32 protrudes from one side of thesupport 31 is used in a power module.

As has been described in the foregoing, with the above electrode members30 and 30 a through 30 f it is possible to relieve thermal stress ateach soldered interface while efficiently radiating heat by applying thecooling mechanism at need. As a result, the occurrence of distortion canbe suppressed and heat cycle resistance and power cycle resistance canbe improved. Moreover, by locating each of the electrode members 30 and30 a through 30 f on a side where an emitter electrode etc. are formed,the surface area and volume of a conductive portion can be increasedcompared with the case of aluminum wire bonding. This enhances a heatradiation effect and lowers electrical resistance. As a result, thegeneration of heat or deterioration in the characteristics of an elementcan be suppressed. In addition, with the electrode members 30 and 30 athrough 30 f the support 31 may be thickened at need. For example, bydoing so, a conventional copper base can be replaced by the support 31.

In the above examples, the case where solder is used for joining membersis described. However, a conductive paste or the like which hardens byheat or light can be used in place of solder. In this case, each of theabove electrode members 30 and 30 a through 30 f can also be used. As aresult, heat can be radiated, and the appearance of a crack can besuppressed by reducing distortion at each interface between membersjoined with a conductive paste.

In the above examples, copper is used as a metal material forfabricating the electrode members 30 and 30 a through 30 f. However,another conductive metal, such as aluminum, having comparatively highthermal conductivity may be used.

In the above examples, electrode members of one type are used in onepower module. However, it is a matter of course that electrode membersof plural types may be used in one power module.

In the present invention, the electrode member in which a plurality ofmetal posts are formed is joined to an electrode of a semiconductorelement. As a result, heat generated in the semiconductor element canefficiently be radiated, and distortion at each interface betweenmembers joined can be reduced by lessening the influence of the thermalexpansivity of materials. Therefore, the appearance of a crack at eachinterface between members joined can significantly be suppressed and asemiconductor device with high reliability can be realized.

The foregoing is considered as illustrative only of the principles ofthe present invention. Further, since numerous modifications and changeswill readily occur to those skilled in the art, it is not desired tolimit the invention to the exact construction and applications shown anddescribed, and accordingly, all suitable modifications and equivalentsmay be regarded as falling within the scope of the invention in theappended claims and their equivalents.

1. A method for fabricating a semiconductor device having asemiconductor element with an electrode on a surface and a electrodemember having a plurality of individual copper or aluminum postsconnected to the electrode, comprising: molding ceramic powder into amolding having a plurality of perforations; burning the molding to forman insulating ceramic member with the plurality of perforations thatpierce through principal planes of the insulating ceramic member;forming the plurality of individual copper or aluminum posts in theplurality of perforations; and connecting each of the plurality ofindividual copper or aluminum posts to the electrode of thesemiconductor element electrically and thermally.
 2. The method forfabricating a semiconductor device according to claim 1, whereinconnecting each of the plurality of individual copper or aluminum poststo the electrode of the semiconductor element electrically and thermallyby a solder layer at an interface between the electrode and theindividual copper or aluminum posts.
 3. The method for fabricating asemiconductor device according to claim 1, wherein forming the pluralityof individual copper or aluminum posts in the plurality of perforationsincludes impregnating the insulating ceramic member with molten copperor molten aluminum.
 4. The method for fabricating a semiconductor deviceaccording to claim 3, further comprising: removing the copper oraluminum formed on the principal planes of the insulating ceramic memberafter impregnating the insulating ceramic member with molten copper ormolten aluminum.